Add colab example (#153)

* Add My first Nowcast example prepared to run in Google Colab.
* Add Run in Colab badge in the readme
* Add a Run your first nowcast! to the documentation's home.

Co-authored-by: Daniele Nerini and Ruben Imhoff

Author: aperezhortal

README.rst

@@ -18,6 +18,8 @@ pySTEPS - Python framework for short-term ensemble prediction systems
       - |license|
     * - community
       - |slack| |contributors| |downloads|
+    * - tutorials
+      - |colab|
 
 .. |docs| image:: https://readthedocs.org/projects/pysteps/badge/?version=latest
     :alt: Documentation Status
@@ -62,7 +64,10 @@ pySTEPS - Python framework for short-term ensemble prediction systems
 .. |downloads| image:: https://img.shields.io/conda/dn/conda-forge/pysteps   
     :alt: Conda downloads
     :target: https://anaconda.org/conda-forge/pysteps
-    
+
+.. |colab| image:: https://colab.research.google.com/assets/colab-badge.svg
+    :alt: Conda downloads
+    :target: https://colab.research.google.com/github/pySTEPS/pysteps/blob/master/examples/my_first_nowcast.ipynb
 
 .. end-badges
 
@@ -75,6 +80,14 @@ The aim of pysteps is to serve two different needs. The first is to provide a mo
 
 The pysteps library supports standard input/output file formats and implements several optical flow methods as well as advanced stochastic generators to produce ensemble nowcasts. In addition, it includes tools for visualizing and post-processing the nowcasts and methods for deterministic, probabilistic, and neighbourhood forecast verification.
 
+
+Run your first nowcast!
+-----------------------
+
+Use pysteps to compute and plot an extrapolation nowcast in Google Colab with `this interactive notebook`__.
+
+__ https://colab.research.google.com/github/pySTEPS/pysteps/blob/master/examples/my_first_nowcast.ipynb
+
 Get in touch
 ============
 

doc/source/conf.py

@@ -235,5 +235,5 @@ def set_root():
 sphinx_gallery_conf = {
     'examples_dirs': '../../examples',  # path to your example scripts
     'gallery_dirs': 'auto_examples',  # path where to save gallery generated examples
-    'filename_pattern': '/*',  # Include all the files in the examples dir
+    'filename_pattern': r'/*\.py',  # Include all the files in the examples dir
 }

doc/source/index.rst

@@ -20,14 +20,15 @@ probabilistic precipitation nowcasting (v1.0). *Geosci. Model Dev.*, **12 (10)**
 __ https://github.com/pySTEPS/pysteps
 __ https://doi.org/10.5194/gmd-12-4185-2019
 
+.. note:: Use pysteps to run your first extrapolation nowcast in Google Colab with `this interactive notebook`__.
+__ https://colab.research.google.com/github/pySTEPS/pysteps/blob/master/examples/my_first_nowcast.ipynb
 
 Documentation
 =============
 
 The documentation is separated in three big branches, intended for different
 audiences.
 
-
 :ref:`user-guide`
 ~~~~~~~~~~~~~~~~~